One modern example of a mobile radio system is the Universal Mobile Telecommunications System (UMTS). The basic architecture of a UMTS mobile radio system has, inter alia, mobile stations (User Equipment (UE)) and a radio access network (UMTS Terrestrial Radio Access Network (UTRAN)). The radio access network contains devices for transmission of data by radio, such as base stations which, in UMTS mobile radio systems, are referred to as node B. The base stations each supply a specific area or a cell in which mobile stations may be located. The interface between a mobile station and a base station, which communicate by radio without the use of wires, is referred to as a radio interface (Uu interface).
The following text includes parts of the technical specification 3GPP TS 25.213, V5.4.0 (2003-09), Spreading and modulation (FDD) and of the technical specification 3GPP TS 25.211, V5.5.0 (2003-09), Physical channels and mapping of transport channels (FDD), for the 3rd Generation Partnership Project (3GPP), Technical Specification Group Radio Access Network.
In a UMTS mobile radio system, digital data to be transmitted is first of all subjected to channel coding. The digital data is, in the process, provided with redundancy and is protected against errors during transmission via a mobile radio channel that is subject to interference, and/or error correction is made possible in the respective data receiver. The digital data is then distributed between physical channels by means of a multiple access method, within the available transmission bandwidth. Finally, the digital data is digitally modulated, in order to be transmitted via a mobile radio channel. The mobile radio channel is subdivided for a transmission mode and for a reception mode, by means of a duplexing method.
The multiple access method used in the UMTS Standard and in the 3GPP Standard (Third Generation Partnership Project) is the code division multiple access method (CDMA), in which a bipolar data bit stream to be transmitted is multiplied by a subscriber-specific bipolar code sequence, and/or by a spreading code, and is spread. The elements of the spreading code are referred to as chips, in order to make it possible to draw a semantic distinction between them and the bits in the data bit stream. In principle, chips are nothing more than bits. The multiplication of the data bit stream by the chip stream results in a bipolar data stream, once again. In general, the rate of the chip stream is a multiple of the rate of the data bit stream, and is governed by the length of the spreading code, which is indicated by a spreading factor (SF). The spreading factor corresponds to the number of chips per bit. If the chip rate on the radio transmission path between transmitters and receivers is constant, the data bit rate that is represented in the chip stream is dependent only on the spreading factor of the respective subscriber-specific spreading code. In the UMTS mobile radio system, orthogonal spreading codes with a variable spreading factor (OVSF=Orthogonal Variable Spreading Factor) are used, in order to make it possible to use variable data rates. The data rate may in this case fluctuate in a range from 32 kbit/s to 2 Mbit/s.
The modulation method used in the UMTS mobile radio system is four-phase keying (QPSK=Quaternary Phase Shift Keying), in which two successive chips in a chip sequence to be transmitted are in each case combined to form a chip pair. A chip pair is in each case mapped on the complex plane onto a symbol in a symbol space which is covered by a real in-phase branch (I) and an imaginary quadrature branch (Q) of the QPSK modulation method, with the symbol having four elements. Owing to the four-value modulation method, two chips are in each case transmitted in each modulation step. The gross chip rate is thus twice as high as the modulation rate.
In the case of UMTS mobile radio systems, the time-division duplexing method (TDD) or the frequency-division duplexing method (FDD) may be used to separate transmission signals and received signals in a base station or in a mobile station, and to separate the uplink from the mobile station to the base station, and the downlink from the base station to the mobile station. In the FDD method, the stations each transmit and receive in separate frequency bands. In this case, the transmission band of one station is the reception band of the other station, and vice versa.
The wideband code division multiple access method (WCDMA) has been chosen by the ETSI (European Telecommunications Standard Institute) as the basis for the FDD-UMTS radio interface (Uu interface), allowing operation at the same data rate in both transmission directions, and symmetrical uplink/downlink operation. According to the UMTS Standard, data is transmitted between the base stations and the mobile stations in time frames. Each time frame in each case has 15 time slots, which each contain 2560 chips. A time frame lasts for 10 ms, so that a time slot has a duration of 666 μs, and a chip has a duration of about 0.2604 μs. The chip rate is 38,400 chips per time frame, or 3.84 Mchips/s.
The multiple access method is used by all the subscribers in order to apply a fingerprint to their payload data by means of a subscriber-specific spreading code, thus allowing the transmitted signal to be reproduced from the sum of the received signals. The bits in the data bit stream can be recovered from the received chip sequence in the receiver by repeating the multiplication process. For this purpose, the chip stream is once again multiplied or correlated, in the correct phase, by the same spreading code which has already been used in the transmitter, thus resulting in the transmitted data bit stream once again.
Different data bit streams, which originate from one transmitter and are intended to be transmitted in parallel are multiplied by different, orthogonal spreading codes, and are then added, in the real in-phase branch and in the imaginary quadrature branch in the QPSK modulation method. The complex sum signal is then also scrambled, which is carried out by complex multiplication of the sum signal, chip-by-chip and based on time frames, by a specific complex scrambling code. In the FDD mode in the UMTS mobile radio system, the scrambling code is station-specific, that is to say each base station and each mobile station use a different scrambling code.
In contrast to the spreading code, the scrambling code is not used for band spreading, but only for orthogonal coding. The scrambling code thus has a fixed length of exactly 38,400 chips, which corresponds precisely to the length of one time frame. Each of these time frames is multiplicatively coded chip-by-chip by an associated scrambling code. Owing to the QPSK modulation method that is used by UMTS mobile radio systems, two bit streams are transmitted at the same time, with each bit stream being coded separately. Two scrambling codes thus exist in each case, a “real” and an “imaginary” scrambling code for the in-phase branch and for the quadrature branch, respectively, in the QPSK modulation method. 224 long scrambling codes each comprising 38,400 chips and 224 short scrambling codes each comprising 256 chips also exist.
FIG. 5 shows a known generator for production of long scrambling codes for the uplink. The chips in the scrambling codes are produced by means of shift registers, with 25 series-connected registers being used in each shift register on the uplink. Information is in each case shifted from an output of one register to an input of a next register by means of a clock signal at 3.84 MHz, which corresponds to the chip rate of 3.84 Mchips/s. The registers are fed back via modulo-2 adders (MOD2), for example exclusive-OR gates (XOR).
The long scrambling codes clong,1,n and clong,2,n are formed by position-by-position modulo-2 addition of 38,400 chip segments of two binary code sequences x and y, which are produced by means of two polynomials. The x code sequence is constructed using a polynomial X25+X3+1. The y code sequence is constructed using a polynomial X25+X3+X2+X+1. The resultant code sequences thus form segments of a set of gold code sequences. The long scrambling code clong,2,n is a version of the long scrambling code clong,1,n which has been shifted through 16,777,232 chips. The binary 24-bit representation of the scrambling code number n is n23, n22, . . . , n0, where n0 is the least significant bit (LSB) and n23 is the most significant bit (MSB). The x code sequence depends on the chosen scrambling code number n, and is referred to as xn. xn(i) and y(i) denote the i-th symbol in the code sequences xn and y, respectively. The code sequences xn and y are constructed as follows.
At the start of the production of the scrambling code, the registers are initialized with predetermined bits. The initial conditions are:xn(0)=n0, xn(1)=n1, . . . , xn(22)=n22, xn(23)=n23, xn(24)=1.  (1)y(0)=y(1)= . . . =y(23)=y(24)=1  (2)
The following recursive definitions apply to successive symbols:xn(i+25)=xn(i+3)+xn(i)modulo 2, i=0, . . . , 225−27.  (3)y(i+25)=y(i+3)+y(i+2)+y(i+1)+y(i)modulo 2, i=0, . . . , 225−27.  (4)
The binary gold code sequence zn is defined by:zn(i)=xn(i)+y(i)modulo 2, i=0, 1, 2, . . . , 225−2  (5)
The real gold code sequence zn is:
                                          z            n                    ⁡                      (            i            )                          =                  {                                                                                                                                                                                              +                            1                                                    ⁢                                                                                                          ⁢                          if                          ⁢                                                                                                          ⁢                                                                                    z                              n                                                        ⁡                                                          (                              i                              )                                                                                                      =                        0                                                                                                                                                                                                      -                            1                                                    ⁢                                                                                                          ⁢                          if                          ⁢                                                                                                          ⁢                                                                                    z                                                              n                                ⁢                                                                                                                                                                                        ⁡                                                          (                              i                              )                                                                                                      =                        1                                                                                            ⁢                                                                  ⁢                for                ⁢                                                                  ⁢                i                            =              0                        ,            1            ,            K            ,                                          2                25                            -              2.                                                          (        6        )            
The real long scrambling codes clong,1,n and clong,2,n are now defined as follows:clong,1,n=Zn(i), i=0, 1, 2, . . . , 225−2; and   (7)clong,2,n=Zn((i+16 777 232)modulo(225−1)), i=0, 1, 2, . . . , 225−2.  (8)
The complex long scrambling code is, finally, defined by:clong,n(i)=clong,1,n(i)(1+j(−1)iclong,2,n(2└i/2┘)),  (9)where i=0, 1, . . . , 225−2 and └ ┘ represents the integer component of the number i/2.
FIG. 6 shows a known generator for production of short scrambling codes for the uplink. The short scrambling codes cshort,1,n (i) and cshort,2,n (i) are defined by a code sequence from the family of periodically extended S(2) codes. The binary 24-bit representation of the scrambling code number n is n23, n22, . . . , n0. The n-th quaternary S(2) code sequence zn (i), 0=n=16,777,215 is obtained by modulo-4 addition (MOD4) of three code sequences, a quaternary code sequence a(i) and two binary code sequences b(i) and d(i), with the initialization of the three code sequences being defined from the scrambling code number n. The code sequence zn (i) whose length is 255 is produced using the following relationship:zn(i)=a(i)+2b(i)+2d(i)modulo 4, i=0, 1, . . . , 254,  (10)with the quaternary code sequence a(i) being produced recursively by means of the polynomialg0(x)=x8+x5+3x3+x2+2x+1, wherea(0)=2n0+1 modulo 4;a(i)=2ni modulo 4, i=1, 2, . . . , 7:a(i)=3a(i−3)+a(i−5)+3a(i−6)+2a(i−7)+3a(i−8)modulo 4, i=8, 9, . . . , 254;   (11)the binary code sequence b(i) being produced recursively by the polynomialg1(x)=x8+x7+x5+x+1, whereb(i)=n8+I modulo 2, i=0, 1, . . . , 7;b(i)=b(i−1)+b(i−3)+b(i−7)+b(i−8)modulo 2, i=8, 9, . . . , 254;   (12)and the binary code sequence d(i) being produced recursively by the polynomialg2(x)=x8+x7+x5+x4+1, whered(i)=n16+I modulo 2, i=0, 1, . . . , 7;d(i)=d(i−1)+d(i−3)+d(i−4)+d(i−8)modulo 2, i=8, 9, . . . , 254;   (13)
The code sequence zn(i) is extended to a length of 256 chips, by setting zn(255)=zn(0). The mapping of zn(i) onto the real binary short scrambling codes cshort,1,n(i) and cshort,2,n(i), where i=0, 1, . . . , 255 is shown in the following Table 1.
TABLE 1Zn(i)Cshort,1,n(i)Cshort,2,n(i)0+1+11−1+12−1−13+1−1
The complex short scrambling code cshort,n is defined by:cshort,n(i)=cshort,1,n(i mod 256)(1+j(−1)icshort,2,n(2└(i mod 256)/2┘))  (14)where i=0, 1, 2, . . . and └ ┘ is the integer component of the number (i mod 256)/2.
Information is transmitted in the uplink from the mobile stations via a radio link to the base stations. The information from various mobile stations is coded using the CDMA multiple access method and transmitted via a common frequency channel or radio channel to those base stations that are in radio contact with the mobile stations in physical channels that are combined to form a radio signal. In the FDD mode a physical channel is defined by the spreading code and by the frequency channel. On the FDD uplink, the physical channels are also distinguished by the phase angle of the carrier signal. Physical channels thus use either a cosine or sine oscillation as the carrier signal. This is achieved by transmitting a different physical channel via the real in-phase branch (I) of the QPSK modulation method than via the imaginary quadrature branch.
A distinction is in general drawn between so-called dedicated physical channels and common physical channels. A dedicated physical channel is used exclusively by one link, and is reassigned when setting up a connection and, possibly, during the connection. Common physical channels are used simultaneously or alternately by a number of links.
Physical channels in the FDD mode are, for example, the dedicated physical data channel (DPDCH), the dedicated physical control channel (DPCCH), the physical random access channel (PRACH) and the physical common packet channel (PCPCH). In addition to the physical channels, indicator channels also exist in the FDD mode. These are single-bit or two-bit messages, which are spread by means of a spreading code and are transmitted at a specific time. An indicator channel is characterized by the spreading code, the frequency channel and the time. Indicator channels are used for notification and for indication of specific events. One example of an indicator channel is the acquisition indication channel (AICH).
The dedicated physical data channel DPDCH exists only on the uplink, and is used for transmission of coded and interleaved payload and signalling data from higher layers of the UTRA protocol stack. One DPDCH, or two or more in parallel, may be used for transmission. If two or more DPDCHs are used in parallel, all of the DPDCHs must have the same spreading factor, and a maximum of six DPDCHs can be transmitted in parallel. In this case, the DPDCHs are distributed as uniformly as possible between the in-phase and quadrature branches of the QPSK modulation method.
The dedicated physical control channel DPCCH is a physical channel for controlling the data transmission between partner instances of the physical layer of the UTRA protocol stack for the uplink. Only information for the physical layer, for example power control commands, transport format indicators or pilot bits, is transmitted via this link. One and only one DPCCH is associated with each layer-1 connection.
The physical random access channel PRACH is used for random access, and exists only on the uplink. The PRACH is used to transmit messages for the random access transport channel (RACH) for the UTRA protocol stack. The RACH may in this case be used both for setting up a call and for transmission of small data packets. One typical operational use for the PRACH is, for example, the request for radio resources in a mobile radio system when a mobile station is setting up a telephone call. Since all of the mobile stations in a cell use the PRACH jointly in order to signal to the mobile radio system that radio resources are required, a specific method must be used to ensure that collisions do not occur between different mobile stations when accessing the PRACH. The method which ensures this is the slotted ALOHA method. Random accesses to the PRACH may take place at defined times, in access time slots. An access time slot corresponds to the duration of 5120 chips, that is to say an access time slot is twice as long as a normal time slot, such as that for a DPDCH. Fifteen access time slots exist within 20 ms and each define one access channel. The random access is subdivided into a competition phase and a transmission phase. In the competition phase, the mobile stations use the slotted ALOHA method to access the PRACH within an access time slot by transmission of a PRACH preamble. In the transmission phase, a PRACH message part is then transmitted.
The common physical packet channel PCPCH is, finally, used for transmission of data packets of the common packet transport channel (CPCH) in the UTRA protocol stack in accordance with a carrier sense multiple access method with collision detection (CSMA/CD). Analogously to the physical random access channel PRACH, the mobile station can start transmission in the PCPCH in specific access time slots. The access time slot in which the mobile station may transmit depends on the current system frame number (SFN).
The scrambling code for scrambling the physical channels DPCCH/DPDCH on the uplink may be either a long or a short scrambling code. When the scrambling code is produced, different code sequences that form a component of the scrambling code are used for the long and the short scrambling code, as defined in the following text. The n-th uplink scrambling code for the physical channels DPCCH/DPDCH, which is referred to as Sdpch,n is defined asSdpch,n(i)=clong,n(i), i=0, 1, . . . , 38,399;   (15)when long scrambling codes are used, and is defined asSdpch,n(i)=cshort,n(i), i=0, 1, . . . , 38,399;   (16)when short scrambling codes are used. The lowest index i in each case corresponds to the chip that is transmitted first in time.
In order to scramble the physical channel PRACH, scrambling codes must be produced for scrambling the PRACH message parts and the PRACH preambles in the PRACH. The scrambling code that is used for the message part of the physical channel PRACH is 10 ms long, and there are 8192 different defined PRACH message scrambling codes. The n-th PRACH message part scrambling code, which is referred to as Sr−msg,n, where n=0, 1, . . . , 8191, is based on the long scrambling code, and is defined as:Sr−msg,n(i)=clong,n(i+4096), i=0, 1, . . . , 38,399;   (17)where the lowest index i corresponds to the chip which is transmitted first in time. The PRACH message part scrambling code corresponds to a scrambling code that is used for the PRACH preamble, or to a PRACH preamble scrambling code. The same scrambling code number is used for both scrambling codes for a PRACH, that is to say if the PRACH preamble scrambling code is Sr−pre,n, then the PRACH message part scrambling code is Sr−msg,n, with the scrambling code number n being the same for both scrambling codes.
The PRACH preamble Cpre,n is a complex sequence formed from the PRACH preamble scrambling code Sr−pre,n and a PRACH preamble signature Csig,s as follows:
                                                        C                              pre                ,                n                ,                s                                      ⁡                          (              i              )                                =                                                    S                                                      r                    -                    pre                                    ,                  n                                            ⁡                              (                i                )                                      ×                                          C                                  sig                  ,                  s                                            ⁡                              (                i                )                                      ×                          ⅇ                              j                ⁡                                  (                                                            π                      4                                        +                                                                  π                        2                                            ⁢                      i                                                        )                                                                    ,                                  ⁢                  i          =          0                ,        1        ,        2        ,        3        ,        …        ⁢                                  ,                  4095          ;                                    (        18        )            where i=0 corresponds to the chip which is transmitted first in time.
The PRACH preamble scrambling code is formed from the long scrambling code. There are a total of 8192 PRACH preamble scrambling codes. The n-th PRACH preamble scrambling code, n=0, 1, . . . , 8191, is defined as:Sr−pre,n(i)=clong,1,n(i), i=0, 1, . . . , 4095.  (19)
The PRACH preamble signature comprises 256 repetitions of a signature Ps(n), with a length of 16 chips, where n=0 . . . 15. This is defined as follows:csig,s(i)=Ps(i modulo 16), i=0, 1, . . . , 4095.   (20)
The signature Ps(n) with the signature number s originates from a set of 16 Hadamard codes of length 16. There are therefore 16 different PRACH preambles, each having 4096 chips, for each access time slot, so that 16 parallel access channels are available for each access time slot, by means of which mobile stations can gain access without any collisions.
A mobile station that wishes to access the PRACH chooses an available access time slot, and then one of the 16 PRACH preambles. The PRACH preamble is then transmitted with a low transmission power, and the station waits for an acknowledgement, which is received via the indicator channel AICH. If no acknowledgement is received from the base station, or the mobile station receives a negative acknowledgement, then it chooses a new access time slot and a new PRACH preamble, and transmits this with a somewhat higher transmission power. This process is repeated until a maximum number of attempts is reached without a positive acknowledgement having been received. When a successful competition phase occurs, that is to say there is a positive acknowledgement, the mobile station transmits its PRACH message with a delay of three or four time slots. The PRACH message bits are transmitted via the real in-phase branch (I) of the QPSK modulation method.
A PCPCH access transmission has one or more PCPCH access preambles with 4096 chips, a PCPCH collision detection preamble with 4096 chips, a PCPCH power control preamble with a length of either 0 or 8 time slots, and a PCPCH message part of variable length, of N×10 ms. The set of scrambling codes which is used for the PCPCH message part has a length of 10 ms, is cell-specific, and each PCPCH message part scrambling code corresponds to the signature and to the access channel element which is used by the PCPCH access preamble. Both long and short scrambling codes may be used in order to scramble the PCPCH message part. There are 64 scrambling codes on the uplink, which are defined per cell, and there are 32,768 different PCPCH scrambling codes, which are defined in the system.
When the long scrambling codes are used, the n-th PCPCH message part scrambling code which is referred to as Sc−msg,n where n=8192, 8193, . . . , 40,959 is based on the long scrambling code, and is defined as:Sc−msg,n(i)=clong,n(i), i=0, 1, . . . , 38,399.   (21)
When the short scrambling codes are used, the n-th PCPCH message part scrambling code, which is referred to as Sc−msg,n, where n=8192, 8193, . . . , 40,959 is based on the short scrambling code, and is defined as:Sc−msg,n(i)=cshort,n(i), i=0, 1, . . . , 38,399.   (22)
The lowest index i corresponds to the chip which is transmitted first in time.
The scrambling code for the PCPCH power control preamble is the same as the PCPCH message part scrambling code. The phase of the scrambling code is chosen such that the end of the code is aligned with the time frame boundary at the end of the PCPCH power control preamble.
The PCPCH access preambles Cc−acc,n,s are complex sequences, in a similar way to the PRACH preambles. The PCPCH access preambles are formed from PCPCH preamble scrambling codes Sc−acc,n and from a PCPCH preamble signature Csig,s as follows:
                                                        C                                                c                  -                  acc                                ,                n                ,                s                                      ⁡                          (              i              )                                =                                                    S                                                      c                    -                    acc                                    ,                  n                                            ⁡                              (                i                )                                      ×                                          C                                  sig                  ,                  s                                            ⁡                              (                i                )                                      ×                          ⅇ                              j                ⁡                                  (                                                            π                      4                                        +                                                                  π                        2                                            ⁢                      i                                                        )                                                                    ,                                  ⁢                  i          =          0                ,        1        ,        2        ,        3        ,        …        ⁢                                  ,        4095.                            (        23        )            
The PCPCH access preamble scrambling code is formed from the long scrambling codes. There are a total 40,960 PCPCH access preamble scrambling codes. The n-th PCPCH access preamble scrambling code, where n=0 . . . , 40,959, is defined as:Sc−acc,n(i)=clong,1,n(i), i=0, 1, . . . , 4095.   (24)
The PCPCH access preamble uses the same 16 signatures as those for the PRACH, although a smaller number of defined code sequences can be used for the PCPCH than for the PRACH. The PCPCH access preamble scrambling code may also be the same as the PRACH preamble scrambling code.
A mobile station that wishes to access the PCPCH first of all uses the access time slots to transmit the PCPCH access preambles before transmitting the actual messages. As already described for the PRACH, these PCPCH access preambles are transmitted with an increasing power level until an acknowledgement is received via the AICH from the base station.
In UMTS mobile radio systems, the base stations (node B) each supply one or more cells in which mobile stations may be located. The base stations process received radio signals from the mobile stations located in their cells, and the mobile stations process radio signals from the surrounding base stations. This processing comprises, inter alia, error correction via the channel coding, spreading and despreading in accordance with the CDMA multiple access method, scrambling as well as modulation and demodulation based on the QPSK modulation method. The base stations and the mobile stations in the UMTS mobile radio system for this purpose each have dedicated data processing devices and at least one central data processing device. The dedicated data processing devices are connected to one another and are connected to the central data processing device such that they can interchange data.
The central data processing device, the dedicated data processing devices etc. are normally provided on a baseband chip. In the case of the base stations and the mobile stations in the UMTS mobile radio system, by way of example, the central data processing device is a digital signal processor (DSP) in order to carry out the complex calculation functions in a communication protocol. The DSP programs the dedicated data processing devices to carry out specific defined functions with the aid of internal locally available registers or memories, which are provided for storage of parameters. The dedicated data processing devices, for example in the case of the UMTS mobile radio system, have a RAKE receiver, a search apparatus or a searcher, a channel decoder and a transmission part. A transmission (TX) modulator is a central block in a transmission part of a UMTS mobile station. The transmission modulator is used to produce the OVSF spreading codes and scrambling codes, for spreading and scrambling of signals on different physical channels, and for processing of the spread signals. The transmission modulator processes not only the dedicated physical data channels DPDCH but also the dedicated physical control channels DPCCH, and produces the scrambling codes for the physical channels PRACH and PCPCH.
The scrambling code Sdpch,n for the dedicated physical data channel DPDCH and for the dedicated physical control channel DPCCH are normally produced using equations 15 and 16, and the preambles Cpre,n,s and Cc−acc,n,s for the physical random access channel PRACH and for the common physical packet channel PCPCH are produced using equations 18 and 23, in separate devices in the baseband chip of a mobile station. The preambles are produced as a function of the respective signature Csig,s using equation 20, in the digital signal processor DSP itself, and are then transmitted to the transmission modulator.
One disadvantage of the production of the scrambling codes and of the preambles in separate devices is that, although this is associated with greater independence for the control of the devices, the complexity, for example with regard to the amount of chip area consumed on a baseband chip, is, however, also greater.
A further disadvantage of the production of the scrambling codes and of the preambles in separate devices is that the production of the signature and of the preamble in the DSP and their transmission to the transmission modulator by means of an additional data transmission are associated with corresponding complexity in terms of power and control.